


Aibreán, aingeal na hÉireann a thit.

by Radiant_Shooketh



Category: Fate/Grand Order, Fate/stay night & Related Fandoms
Genre: Angst and Tragedy, Bittersweet Ending, F/M, Forgive Me, Gen, I am also a sadist, I am bad at tags, I like these type of sibling relationships in fiction, I love Cú Chulainn too much, i am a masochist, pls help
Language: English
Status: Completed
Published: 2021-02-22
Updated: 2021-02-22
Packaged: 2021-03-12 19:53:21
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,455
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29639784
Author URL: https://archiveofourown.org/users/Radiant_Shooketh/pseuds/Radiant_Shooketh
Summary: Title translation: April, the fallen angel of Ireland.I had this idea in my mind for awhile. What if Cú Chulainn had a twin sister? And thus this oneshot was born. Cú Chulainn and Aibreán's tales told in a jumbled mess. Please enjoy this trash. This might turn into a series, who knows.
Relationships: Cú Chulainn | Lancer/Other(s)
Kudos: 3





	Aibreán, aingeal na hÉireann a thit.

A long time ago, there were these twins…

They were as close as siblings could be. The boy with blue hair and ferocious red eyes protected his little sister fiercely. Whenever the other kids would dare attempt to bully her, he was on them like a beast, beating them up until they apologized. To summarize, he was described as the best brother.

The girl with the same blue hair and sparkling soft red eyes adored her big brother. She wanted to be strong and mighty like him. She looked up to him, saw him as a role model and most importantly, as her hero. She saw him as perfect, and wanted to be just like him. Someday, she wanted to protect him like he’d always done for her.

Because of their father, they were born with incredible abilities and knowledge in several fields. They were both divine beings, demigods. As such, people saw them as remarkable individuals.

In their country, there was this boy troop, a place where boys could train to become soldiers and defend their nation. As such, the brother joined. The sister insisted on joining as well, but as the name implies, it was meant for boys only. Discouraged, the sister could only watch as her brother trained alongside other boys as they became warriors. Her brother was known as the best of the best in the troop. Around this time, it could be safe to assume that a sort of rivalry was formed between the twins. While the brother was training to be a warrior, the sister was encouraged to be educated in more feminine hobbies. Begrudgingly, she had no choice and relented. While she was busy sewing or learning about to bear children or find a suitable husband, she would watch bitterly as her brother made a name for himself within the troop.

One day, both their lives would change forever…

Tragedy struck when the boy accidentally killed the ferocious guard dog that guarded the house of a blacksmith. The girl had run to see what all the commotion was about and she could only stare incredulously at the corpse of the large dog. Her brother had apologized and sworn to take care of the puppies of the guard dog if it did have any, but the blacksmith turned down the offer and insisted for the boy to become stronger first. The king of their nation had declared that her brother would be the shield of their country. Right then and there, he was sworn in to the Knights of the Red Branch, defenders of their kingdom. After hearing that, the sister had asked the king to be a Knight as well, but the king turned her down swiftly. Furious, she desperately went to her brother and asked for help.    
  
  
“Help me convince Uncle that I can join the Red Branch. Please, Sétanta.”

Her brother refused, explaining that only men could join the Red Branch. They fought for a while about this. Who cares if she was a woman, she had insisted. She was just as capable at becoming a knight as he was. They were both blessed with incredible abilities and with proper training, she could be as strong as he was. The brother refused again and said that it was too dangerous for a woman to be on the battlefield. Clearly having lost the argument, the sister stopped and the twins ceased fighting. From that day on, her brother was known as Cú Chulainn.

It was at that moment that the sister would harbour jealousy and hate for her brother, one that would last for the rest of her life...

The path for the sister looked very dull compared to her brother. A druid had predicted that her brother's life would be cut short as a hero. He simply laughed it off, accepting his fate with open arms. The sister considered her options: would she prefer to live a long boring life or a short life filled with adventure and glory? Like her brother, she wanted to be well known as a hero who people could look up to the way she had looked up to her brother all her life. But what could she do now? Girls weren’t allowed to be warriors. 

Several years had passed. Her brother was well known in their community and was an adored member of the Red Knight Branch. One day over a meal, her brother was talking about a beautiful girl that he had met and proclaimed that he loved her and wanted her hand in marriage. The sister could only scoff bitterly. 

Over the years, their relationship had gotten pretty bad. The brother would try to talk to his sister, but she would give curt responses or simply ignore him entirely. He had no idea why she was acting this way, but he never gave up and always tried talking to her, despite her bitterness towards him. 

One day, her brother said that he would be making a trip to Alba. The sister silently watched as her brother packed his things up and before she knew it, he was off on his chariot. She had asked her foster father why he was going. Apparently, it was to meet Scáthach, a famous Scottish warrior woman and be trained under her so that he can marry Emer. That was one of the conditions that she had set up for her brother so that they would marry. He had eyes for only Emer despite all of the girls in their country practically throwing themselves at his feet. It was the same for her. All the men were begging for marriage, but she had swiftly turned them all down. 

It would be several years later that she would see her brother again… 

The sister’s jealousy and bitterness towards her brother only got worse when he returned from his trip. He would become Scáthach’s best pupil, and she gifted him with her most powerful weapon. A demonic spear that would emit many barbs and inflict a deadly injury upon the victim. People sang praises about her brother. People celebrated him as a fearsome warrior who would bring glory to Erin. He was their pride and joy. Because of his fulfillment, he and Emer got married, the sister blatantly refusing to attend their wedding on that day. The brother was hurt that his sister wasn’t there to celebrate his accomplishments, and he didn’t know why. She refused to give any praises to her brother. Didn’t he receive enough of those? She was sick of hearing how godly and mighty her brother was. 

One day, their kingdom was attacked by the army of Connacht, a neighbouring kingdom ruled by Queen Medb. While the women and children were forced to retreat and seek refuge in their homes or in the castle, her brother and other soldiers were sent to deal with the army. Of course, she had given up on trying to convince anyone that she could fight so she could only watch as her brother single-handedly defended Ulster. Somehow, a sickness plagued the other soldiers with labour pains. Since she and her brother weren’t born in Ulster, he wasn't affected by the curse and he challenged every soldier in single combat, winning all of them. Queen Medb used dirty tricks and eventually, made her brother fight his best friend who also trained with him in the Land of Shadows, and killed him.

Peace settled in Ulster for many years. Her brother was hit by depression ever since killing his best friend and the sister felt a sick sense of joy and satisfaction settle within her. It was good seeing him down in the dumps for once, not seeing that stupid smug and cheeky smile on his face. At some point, their foster father had left them and pledged allegiance to Queen Medb after their uncle had killed his sons. Her brother soon got over his best friend’s death and enjoyed life with his friends and wife, all while still trying to talk to his sister. 

One day, a kid was causing trouble for the Red Branch. 

She had heard about it from one of the soldiers, who was reporting to the king. The king ordered her brother to go deal with this troublesome intruder. She watched as Emer had cried and told him not to go but he couldn’t refuse a royal order, so he had no choice. The sister was genuinely shocked to hear stomping outside her door, followed by a door slamming. Her brother… She had gone outside and Emer, followed by her uncle and other soldiers looked grim. Emer was crying. 

“What is going on?” The sister asked. 

Emer explained everything. 

Back in her room, the sister almost burst into laughter. Her brother had sired a child with Aífe? That was rich. What did he say those many years ago? That he had only eyes for Emer? What a joke. Her brother was no different than any other man. His lust was powerful, though it was completely normal for men in this country to have multiple relationships with other women. She had secretly hoped her brother was different, but apparently not. He was drunk on lust. This was simply karma getting back at him. A deep satisfaction settled in her chest at the thought of her brother suffering such agony, having to kill his own son unknowingly. 

The sister made a promise to herself that day…

  
She spent a few days preparing all her belongings. Erin had nothing left for her now. She couldn't become a hero here, so she would have to go somewhere else to make a name for herself. Hoping not to run into anyone, she discreetly made her way to the exit with her travelling pack. Unfortunately, she ran straight into her brother on her way to the castle’s entrance. 

“Aibreán? Where are you going?” 

“Away,” she answered coldly and walked past him. 

“Wha-” He swiftly turned around and grabbed her hand. 

“Let go, Sétanta.” She slapped his hand away.

“Where are you going?” He asked again. 

Aibreán took a good look at her brother, the first time she really did so in a long time. He looked positively terrible. He had dark circles under his eyes and he looked very exhausted. Clearly, he hasn’t slept right in a few days, and his eyes looked very sunken. She’d never seen her brother cry but the evidence was all over his face. 

“Alba.”

“Wait, why are you going to Alba?”

“I am moving to Alba. I’ve got nothing here in Ulster, so I am moving there to make a name for myself. I can’t be a hero here. Ulster has you. They never saw anything in me other than being a good wife, so I am leaving. Ulster will be fine without me.” Aibreán admitted the last part painfully, but it was true. Ulster would not remember her at all. Her chest hurt. Aibreán turned away and headed for the exit. 

“Wait Aibreán, you can't just leave!”

“Watch me!” 

“Please, you can’t leave… You can't leave me. I need you, Aibreán.” 

That made her snap. “Where were you when I needed you the most, Sétanta? Huh?! When I wanted to join the boy troop and Red Branch, where were you when I needed you then?! You were never there for me, so why should I be there for you now when you need me the most? Where were you when I needed you? You left me to be a hero, that’s what! You don’t need me, so I clearly don't need you!”

“What do you mean? Of course I need you. It’s just that…'' He didn’t have an answer to her previous questions. Where was he when she needed him the most? He wasn’t there, she was right. He abandoned her to become a famous hero. It hurt his soul to hear his beloved little sister say that she didn’t need him. But he had nothing else to say. He had nothing to defend himself. 

“That’s what I thought,” Aibreán said. She left Ulster that day, never to be seen by anyone again. Everyone was in disbelief and shock over Aibreán leaving. The grief of killing his son and best friend, as well as losing his sister to his own hubris almost drove Cú Chulainn insane and Ulster feared that he would turn against his allies. The druids were ordered by the king to place him under a spell and make him fight the sea, thinking they were an army so that he could let out his frustration on some waves.

And Aibreán?

She travelled to Alba and sought out Scáthach in the Land of Shadows. The teacher was clearly shocked that Cú Chulainn’s sister would seek her out so desperately like this, but she trained her anyway. Aibreán demanded to be handed a powerful weapon like how she had given to her brother but the mistress of the Land of Shadows refused, sensing a darkness within her latest pupil’s heart. Furious, Aibreán left the Land of Shadows and headed towards the kingdom in a fury. Before arriving there, Aífe had heard about Cú Chulainn’s twin sister in Alba. She found the young girl and offered to train her as well. They bonded over how foolish Cú Chulainn was and their shared frustration and pain and rage caused by him fuelled their hate and vengeance. 

Soon enough, stories were going around that a strong warrior was residing within the Kingdom of Alba. The king took her in and seeing her prowess in battle, appointed her as the head of his army. Aibreán made her name as a hero of Alba who protected the kingdom from invaders. She was known for her ferocity and swiftness on the battlefield, very unforgiving to enemies of Alba. Even her own allies found her terrifying. But because of that, the kingdom settled into many years of peace. During those times, Aibreán got married and even had a daughter. Aibreán finally got her wish: to be seen as a hero who people looked up, and to be respected and loved for who she was. 

Cú Chulainn was Erin’s Child of Light, then it could be said that Aibreán was Alba’s Child of Light. While he lived a short life, Aibreán lived a relatively long and happy and peaceful fight. But even with her wish fulfilled, Aibreán would never forgive her brother for abandoning her, and not supporting her. She carried that hatred to her grave, and it would drastically affect things later on. 

“Servant, Avenger. My name is Aibreán, the fearsome Spear of Alba… Please give me your orders, Master. I look forward to working with you.” 

**Author's Note:**

> Add me on FGO because I need more friends (I desperately need a Cú Alter at NP5 if y'all have him lmao)
> 
> Friend code: 293,215,958


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